Hydraulic Vane Pumps. In a vane-type pump, a slotted rotor splined to a drive shaft rotates between closely fitted side plates that are inside of an elliptical- or circular-shaped ring. Pumping chambers are formed between succeeding vanes, carrying oil from the inlet to the outlet. CHIEF V20 Vane Pumps V20-1P9P-1A11: 1.81 CID, 9 GPM, 3000 Max PSI, 2800 Max RPM, 1.25 NPT, Inlet, 3/4 "NPT outlet ports, CW rotation, 256148 How does a vane pump work: The rotor is sealed into the cam by two sideplates. Vanes or blades fit within the slots of the impeller. As the rotor rotates (yellow arrow) and fluid enters the pump, centrifugal force, hydraulic pressure, and/or pushrods push the vanes to the walls of the housing. Fluid then exits the discharge port.